Analysis of molten materials

ABSTRACT

THIS INVENTION CONCERNS MOLTEN MATERIAL ANALYSIS APPARATUS IN WHICH THERE IS MEANS FOR REDUCING OR PREVENTING BUILD UP OF PARTICULATE MATERIAL SAMPLE ON THE WALL OF A CONDUIT CARRYING SAID SAMPLE FROM AN ATOMIZER WHICH EXTRACTS THE SAMPLE FROM A MELT TOWARDS AN ANALYSIS STATION. THE INVENTION ALSO CONCERSN PLASMA JET APPARATUS FOR ANALYSING A PARTICULATE SAMPLE WHICH APPARATUS HAS MEANS FOR PREVENTING SAMPLE BUILD UP BETWEEN THE DELIVERY END OF A CONDUIT FEEDING THE SAMPLE TO THE APPARATUS AND A PROXIMATE ELECTRODE OF THE APPARATUS.

Sept. 20, 1971 R. v. WlLLlAMS ET ANALYSIS OF MOLTEN MATERIALS Filed Sept. 29, 1969 3 Sheets-Sheet 1 K 10 d 4 2 8 I g 1: I

Sept. 20, 1971 ILLIAMS ETAL 3,606,540

. ANALYSIS OF MOLTEN MATERIALS Filed Sept. 29, 1969 3 Sheets-Sheet 2 Sept. 20, 1971 R. v. WILLIAMS ETAL 3,606,540

ANALYSIS OF MOL'IEN MATERIALS Filed Sept. 29, 1969 E SheetS-Sheet 3 United States Patent 0 3,606,549 ANALYSIS OF MOLTEN MATERIALS Royson Vaughan Williams, Staines, Bruce Bennett Fulford, Harrow, and Edmund Arthur du Bois, Purley, England, assignors to The British Iron and Steel Research Association Filed Sept. 29, 19659, Ser. No. 861,929 Claims priority, application Great Britain, May 23, 1969, 26,554/ 69 Int. Cl. G01j3/30, 3/42 U.S. Cl. 35686 9 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with apparatus for analysing of molten materials, for example molten metals.

In our British patent specification No. 1,116,052, we have disclosed apparatus for analysing molten material which apparatus comprises (a) means for withdrawing material particles from a body of molten material to be analysed, and (b) an analysis device for analysing said particles.

The present invention is concerned with improvements in the said elements (a) and (b) and with the provision of a continuous analysis apparatus incorporating these improved elements.

According to the present invention in one aspect, there is provided apparatus for analysing molten material comprising: atomizer means for extracting material in particulate form from a melt of such material; a tube forming part of the atomizer means one end of which is adapted to contact the melt; means for supplying an atomizing gas to the other end of the tube to cause the formation of material particles from the melt which material particles pass along the tube to said other end; a conduit located downstream of said tube for receiving therefrom a stream of atomizing gas and material particles; an analysis device for receiving material particles from the conduit and analysing the same; and means for supplying a gas barrier free of said material particles between the stream of atomizing gas and material particles, and the inner surface of the conduit to reduce build up of material particles on the said inner surface.

According to the present invention in another aspect, there is provided a continuous analysis apparatus comprising: a sampling probe consisting of atomizer means for extracting material in particulate form from a melt of such material; a tube forming part of the atomizer means one end of which is adapted to contact the melt; means for supplying an atomizing gas to the other end of the tube to cause the formation of material particles from the melt which material particles pass along the tube to said other end; a conduit located downstream of said tube for re ceiving therefrom a stream of atomizing gas and material particles; and means for supplying a gas barrier free of said material particles between the stream of atomizing gas and material particles, and the inner surface of the conduit to reduce build up of material particles on the said inner surface; a plasma jet apparatus comprising: a

region in which there are electrodes between which an arc will be struck; a conduit for receiving material particles from the atomizer means and for delivering said material particles to said region, said conduit having a delivery end proximate one of the electrodes; and means for delivering gas between the delivery end of the conduit and said one electrode to prevent build up of said material particles in the region of said one electrode; a first line along which a stream of atomizing gas and material particles will pass from the sampling probe; second and third lines communicating with the first line, the plasma jet apparatus being in the second line so that a portion of the material particles will pass along the second line into and out of the plasma jet apparatus, the third line being arranged to cause the balance of the material particles to by-pass the plasma jet apparatus; a fourth line downstream of the junction between the second and third lines for delivering the stream of atomizing gas and material particles to a filter for removing the material particles; a fifth line for delivering the filtered atomized gas to a compressor and cooler; a sixth line for delivering the cooled atomized gas under pressure to the sampling probe; and an analysis device for analysing the arc produced by the plasma jet apparatus.

The present invention will be more readily understood from the following description, given by way of example only, reference being made to the accompanying drawings in which line reference numerals indicate like parts and in which:

FIGS. 1 to 4 are sectional views of different forms of atomiser of the invention for withdrawing material particles from a body of molten material to be analysed;

FIG. 5 is a sectional view of a plasma jet source of the invention for analysing the withdrawn particles, and

FIG. 6 shows schematically a continuous analysis apparatus.

Broadly speaking, in our British patent specification No. 1,116,052, the means (atomizer) for withdrawing material particles from a body of molten material (a melt) to be analysed comprises a conduit, and means for feeding a gas under pressure adjacent an end of the conduit to detach molten material particles from a melt when the conduit end is adjacent thereto and to drive the particles along the conduit. Unless steps are taken to prevent it, the gas under pressure will drive still molten particles towards the inner surface of the conduit and because these particles are still molten they will stick to this surface and there will be a build up of the material on this surface of the conduit. Such build up has a number of undesirable effects. Firstly, it affects the size of particle withdrawn from the melt. The mean particle size should lie within a certain range (mentioned later) in order that an accurate analysis can be made by the analysis device. Particle build up on the conduit will result in particles passing to the analysis device which are outside this range. Secondly, the particle build up would have an adverse effect on the analysis results of a material differing from that constituted by the particle build up; thus the same conduit could not be used satisfactorily for the analysis of particles from melts of different materials. Thirdly, continued build up or deposition inhibits and can actually prevent sample atomization.

The atomizers of FIGS. 1 to 4 are so designed that such build up of spray particles is prevented or at least reduced to an extent which can be tolerated.

Turning to FIG. 1, the atomizer 10 comprises an atomizer head 11 downstream of which and spaced therefrom is a conduit 12 for carrying the particles towards an analysis device. Within the head 11 and extending downwardly therefrom is a tube 13 the open end 14 of which is below the surface 15 of the liquid material, for example metal, which is to be analysed. Over a part of its length adjacent its other open end 16, the tube .13 is spaced from an internal surface 17 of the head 11 to provide an annular space 18. Atomizing gas (which may be an inert gas) under pressure enters the space 18 by way of duct 20 concentric with tube 13. The atomizing gas leaves the space 18 at high speed adjacent the open end 16 of the tube with the result that material is drawn up the tube 13 and atomized into particles by the atomizing gas. These particles, together with the atomizing gas in which theye are entrained, move in the direction indicated by the arrows 21.

Space 22 separates conduit 12 from head 11. The rapidly moving stream of atomizing gas and particles will entrain outside air into this space as indicated by the arrows 23. This outside air will thus be drawn into the conduit 12 and in particular will enter the annular space 24 between the stream of atomizing gas and particles and the inner surface 25 of the conduit 12. This outside air will provide a gas barrier free of said material particles between the stream of material particles and atomizing gas and the inner surface 25 to prevent, or reduce to a tolerable level, build up of spray particles on the surface 25. It may be that spray particles may eventually contact the surface 25 but by this time they will have solidified and therefore will not stick to and thus build up on this surface but instead will be reflected off into the main stream.

The geometry of the atomizer of FIG. 1 can be made such that the atomizer produces atomized particles of any liquid metal of the desired mean size (within a range of -150 micrometers mean particle dia.) for analysis in a plasma arc. The limits of the design variables of the atomizer of FIG. 1 and also, where applicable, of the atomizers of FIGS. 2 to 4 are:

(i) Internal diameter D of liquid jet tube 136 mm. to 13 mm.

(ii) Diameter of at surface 178.5 mm. to 16 mm.

(iii) Outside diameter of liquid jet tube 137.5 mm. to mm.

(iv) Metal fiow rates-0.3 kg./hr. to 2 kg./hr.

(v) Atomizer gas pressures0.3 M.N./rn. to 0.6 M.N./m.

(vi) Negative liquid head H0 ems. to 14 cms.

In the atomizer 10 of FIG. 2, the atomizer head 11 is the same as the head 11 of FIG. 1 but the conduit 12 of the atomizer of FIG. 2 is integral with the head 11. Build up of spray particles on the inner surface of the conduit 12 of the atomizer of FIG. 2 is prevented or at least reduced to a tolerable extent by placing secondary jets of gas in the wall of conduit 12 to deflect the spray particles away from surface 25. As illustrated, the wall of conduit 12 has two sets 26, 27 of slots which are fed with gas under pressure from annular manifolds 28, 30 respectively. It will be noted that the slots 26,, 27 are inclined in the direction of arrows 21 indicating the direction of travel of the stream of material particles and atomizing gas, such inclination of the slots 27 exceeding such inclination of the slots 26. The gas for passage through the slots 26, 27 can be supplied from the same source of gas that is used to atomize the liquid material which may be metal. The gas issuing from the slots 26, 27 provides a gas barrier free of said material particles between the stream of material particles and atomizing gas and the inner surface of conduit 12 to prevent, or at least reduce to a tolerable extent, build up of spray particles on the surface 25.

FIG. 3 shows a venturi atomizer 10 in which the wall 25 of conduit 12 is shaped to a venturi pattern in order to reduce the degree of turbulence in the stream of material particles and atomizing gas which pass down the conduit 12 commencing at the end 16 of the tube 13, whereby build up of spray particles on the surface 25 is prevented or at least reduced to a tolerable extent. The length 31 of tube 13 adjacent its end 16 is placed in the venturi throat 32 and there is defined an annular passage 33 surrounding this portion of the tube 13. Atomizing gas under pressure enters the passage 33 by way of passages 34 and inlet ports 35. This atomizing gas as well as atomizing the molten material drawn up through the tube 13 also provides a gas barrier free of said material particles between the stream of material particles and atomizing gas which will pass down conduit 12 and the inner surface of conduit 12 to prevent, or at least reduce to a tolerable extent, build up of spray particles on the surface 25.

The atomizer of FIG. 4 is a modification of that of FIG. 3, the modification comprising splitting the annular passage 33 into two annular passages 36, 37 by means of a ring 38. The spray particles in the FIG. 4 atomizer will be constrained to flow along an axial path by means of the secondary gas flow issuing from the (secondary) annular passage 37 enclosing the atomizing annular passage 36, whereby build up of spray particles on the surface 25 is prevented or at least reduced to a tolerable extent. Also, the gas issuing from the annulus 37 provides a gas barrier free of said material particles between the stream of material particles and atomizing gas and the inner surface of conduit 12 to prevent, or at least reduce to a tolerable extent, build up of spray particles on the surface 25.

In any of the atomizers of FIGS. 1 to 4, the spray particles can be constrained to flow along an axial path (thereby being kept away from the inner surface of the conduit 12) by applying suction to the conduit 12 at a location remote from the location of atomization.

A further feature of the atomizers of FIGS. 1 to 4 is that the cold (secondary) gas which is introduced into the conduit 12 will promote rapid freezing of the spray particles. This itself reduces the build up of spray particles on the inner surface of conduit 12.

In any of the atomizers of FIGS. 1 to 4, any part of the atomizer which will be adjacent, or in contact with, the hot molten material may be protected by replaceable rings of refractory brick.

The particulate lrnaterial from any of the atomizers of FIGS. 1 to 4, can be analysed spectrographically by being entrained in a plasma jet. Such a jet producing apparatus is shown in FIG. 5. The stream of material particles (which will now of course be solid) and atomizing gas passes along a transfer pipeline from the conduit 12 and enters the plasma jet apparatus by way of an insulated sample tube 40 which may be made of glass. After leaving the tube 40, the particles pass between an annular anode 41 and an annular cathode 42 between which an arc is struck. The are may be stablised by a cathode counter electrode 43. Cooling water for the anode is fed into chamber 44. The provision of the insulated sample tube 40 up which the particulate sample passes eliminates back-arcing of the plasma jet.

'Undesirable build up of the particulate sample in the region of the anode 41 is prevented by the provision of additional gas (which may be inert gas) to the plasma jet. This additional gas under pressure enters the apparatus by way of inlet 45 and discharges as indicated by the arrows 46 into the space between the anode and end 47 of tube 40. Build up of the particulate sample in the region immediately below the anode has two undesirable effects, namely: (a) the drawing into the plasma jet of further sample particles will be prevented, and (b) material from the built-up sample would become reentrained in the gas stream of another sample and would effectively contaminate that other sample.

The plasma are 48 is stabilised by means of gas (which may be inert) which enters through tangential inlet 50 into the chamber housing the anode 41 and cathode 42.

A spectrograph (not shown) will be connected to the plasma jet apparatus by way of coupling 51 whereby the spectra from the arc can be analysed and the content of The hot sample will be cooled after leaving the are 48 by means of a water jacket 52.

Turning to the continuous analysis apparatus of FIG. 6, the atomizer which is in effect a sampling probe and which may comprise any of the atomizers of FIGS. 1 to 4 is shown at 53. The stream of atomizing gas and sample particulate material or dust leave the probe 53 along line -4. A filter may be located at 5-5 to remove any particles of a size lying outside the range desired for analysis. The line 54 divides at 54; one branch 56 takes a portion of the sample to the plasma jet apparatus 57 and the other branch 58 takes the rest of the sample past the apparatus 57. A spectrograph 60 is shown coupled to the apparatus 57. The branches 56, 58 come together at 61 and the combined stream passes, by way of line 62, through dust filter 63 which removes all the particulate material from the stream. The atomizing gas 'with the particulate material removed therefrom passes to a compressor and cooler 64 via line 65. The atomizing gas leaves the compressor and cooler 64 by line 66 which delivers the gas to the probe 53; the cycle is then repeated.

Examples of metals which can be analysed by the apparatus of the present invention are steel, basic iron, aluminium and copper. The atomizing gas can be any inert gas, for example argon.

The said gas barrier between the stream of atomizing gas and material particles and the inner surface 25 of the conduit 12 should be inert if it is desired to measure nonlmetallic elements by analysis.

The probe 53 could be placed in a still body of molten material, for example in a steel furnace, or could be placed in a moving flow of molten material.

What is claimed is:

1. Apparatus for analysing molten material comprismg:

atomizer means for extracting material in particulate form from a melt of such material;

a tube forming part of the atomizer means one end of which is adapted to contact the melt;

means for supplying an atomizing gas to the other end of the tube to cause the formation of material particles from the melt which material particles pass along the tube to said other end;

a conduit located downstream of said tube for receiving therefrom a stream of atomizing gas and material particles;

an analysis device for receiving material particles lrom the conduit and analysing the same; and

means for supplying a gas barrier free of said material particles between the stream of atomizing gas and material particles, and the inner surface of the conduit to reduce build up of material particles on the said inner surface.

2. Apparatus according to claim 1, wherein the conduit is spaced from the atomizer means to allow for the entry of gas outside the apparatus into the conduit to provide said barrier.

3. Apparatus according to claim 1, wherein the conduit wall is apertured to allow for the entry thereinto of gas which will provide said barrier.

4. Apparatus according to claim 1, wherein the inner surface of the conduit is venturi-shaped and has a throat and wherein the atomizer means comprises a hollow member having one open end into which molten material will be drawn and an open end located in the region of the conduit throat and spaced from the throat to define therebetween a passage for atomizing gas whereby material will be withdrawn from said hollow member open end in particulate form, the venturi-shape of the inner surface of the conduit having in use, a reducing effect on the degree of turbulence in said stream. which will pass down the conduit downstream of said open end of the hollow member to reduce or prevent said material build up and the arrangement being such that a portion of the atomizing gas which will pass through said passage will provide said barrier.

5. Apparatus according to claim 4, including a ring located in said passage and spaced both from said hollow member and said throat so as to divide said passage into an atomizing gas passage and a secondary gas passage.

6. Apparatus according to claim 1 including plasma jet apparatus comprising a region in which there are electrodes between which an arc Will be struck, a conduit for receiving material particles from the atomizer means and for delivering said material particles to said region, said conduit having a delivery end proximate one of the electrodes, and means for delivering gas between the delivery end of the conduit and said one electrode to prevent build up of said material particles in the region of said one electrode, the analysis device being adapted to analyse the arc produced by the plasma jet apparatus.

7. Plasma jet apparatus according to claim 6, wherein said conduit is made of glass.

8. Continuous analysis apparatus comprising:

(a) a sampling probe consisting of:

(1) atomizer means for extracting material in particulate form from a melt of such material,

(2) a tube forming part of the atomizer means one end of which is adapted to contact the melt,

(3) means for supplying an atomizing gas to the other end of the tube to cause the formation of material particles from the melt which material particles pass along the tube to said other end,

(4) a conduit located downstream of said tube for receiving therefrom a stream of atomizing gas and material particles, and

(5) means for supplying a gas barrier free of said material particles between the stream of atomizing gas and material particles, and the inner surface of the conduit to reduce build up of material particles on the said inner surface;

(b) a plasma jet apparatus comprising:

(1) a region in which there are electrodes be tween which an arc will be struck,

(2.) a conduit for receiving material particles from the atomizer means and for delivering said material particles to said region, said con-- duit having a delivery end near one of the electrodes, and

(3) means for delivering gas between the delivery end of the conduit and said one electrode to prevent build up of said material particles in the region of said one electrode;

(c) a first line along which a stream of atomizing gas and material particles will pass from the sam pling probe;

(d) second and third lines communicating with the first line, the plasma jet apparatus being in the second line so that a portion of the material particles will pass along the second line into and out of the plasma jet apparatus, the third line being arranged to cause the balance of the material particles to by-pass the plasma jet apparatus;

(e) a fourth line downstream of the junction between the second and third lines for delivering the stream of atomizing gas and material particles to a filter for removing the material particles;

(f) a fifth line for delivering the filtered atomized gas to a compressor and cooler;

(g) a sixth line for delivering the cooled atomized gas under pressure to the sampling probe; and

(h) an analysis device for analysing the arc produced by the plasma jet apparatus.

9. Apparatus according to claim 8 including a filter located in said first line.

(References on following page) 10 Continuous Ultrasonic Nebulization and Spectro- 7 References Cited UNITED STATES PATENTS 2/1967 Thorpe 35685 9/1969 Greenfield et al 356-85 5 12/1969 Rendina 356-85 7/1970 Kroeger et a1. 356-106 OTHER REFERENCES 8 graphic Analysis of Molten Metals; Fassel et 211.; Analytical Chemistry; vol. 40 1; January 1968, pp. 247- 249.

RONALD L. WIBERT, Primary Examiner V. P. MCGRAW, Assistant Examiner US. Cl. X.R. 35 696 

